1. Field of the Invention
The invention relates to a cutter hub holder for blades acting against a die plate of an underwater pelletizer including a resiliently biased blade holder that is drivingly connected with a driven shaft and biased axially toward the die plate at a variable controlled pressure. In one embodiment of the invention, the driving connection between the shaft and blade holder includes a bayonet quick connect and disconnect drive coupling including an axially movable key and groove drive connection. In another embodiment of the invention, the driving connection between the shaft and blade holder includes an axially movable key drive connection.
2. Description of the Prior Art
The following U.S. patents and German document relate to developments in underwater pelletizers.
2,432,734 4,123,207 5,059,103 3,196,487 4,179,255 5,110,523 3,317,957 4,500,271 5,148,831 3,353,213 4,529,370 5,190,768 3,832,114 4,614,307 5,435,713 3,912,434 4,728,276 5,527,176 German Document 2,638,126
The above patents disclose (a) an arrangement that manually controls displacement of the cutter assembly to compensate for blade wear and maintain the proper blade-to-die pressure, (b) an arrangement that automatically advances the blade by a stepping motor activated by a sensor that detects blade wear by sensing the relative distance between the cutter assembly and the die, (c) a spring that exerts pressure against the knife holder assembly, (d) electronic circuits for controlling hydraulic pressure to automatically displace the drive shaft and thereby control blade-to-die pressure, and (e) an arrangement that includes a pressure chamber receiving fluid pressure through a bore in a drive shaft to bias the cutter blades toward the die plate. However, the above patents do not disclose a structure which delivers variable pneumatic or hydraulic pressure to a piston and cylinder incorporated into the drive shaft to an intermediary member which, in turn, exerts a force against a spring or other resilient member or material that axially displaces the cutter assembly or cutter hub to maintain optimum pressure on the cutter blades toward the die face. Also, the above patents do not disclose a bayonet coupling cutter hub attachment to the drive shaft of an underwater pelletizer which permits relative axial movement therebetween.
In a cutter hub holder of this type, such as generally disclosed in U.S. Pat. No. 5,059,103 issued Oct. 22, 1991, the cutter hub is pressed against the die plate by a spring, in order to compensate for wear of the cutting blades and to ensure a permanent contact of the cutting blades with the die plate. In the known cutter hub holder, the spring pressure is selected to satisfy the needs during pelletizing. This pressure force is thus always set to the highest pressure required during operation, while there are phases in operation, during which a lower spring force would be sufficient. Yet, the higher the spring pressure acting on the blade holder, the greater the wear of the blades and of the die plate.
Any equipment utilizing manual adjustment methods for the cutter holder and blades requires considerably more operator attention while the equipment is running. As the blades wear, the pellet quality decreases causing the operator to constantly monitor the process and adjust the blades. The amount of adjustment that is made will vary from one operator to the next. Often the tendency is to over adjust, causing premature blade and die wear. The present invention uses constant, controllable fluid pressure, pneumatic or hydraulic, to continually adjust the cutter blades. The pressure can be set as light or as heavy as required allowing the operator to make one setting with no further adjustment required. A compression spring or other resilient member or material is used in the cutter head to assure constant contact between the die and cutter.
Cutter hub holders utilizing a compression spring alone to adjust the blades offers no flexibility for varying the pressure of the cutter blades against the die face. A spring of the desired tension must be installed in the cutter head during setup. Once the machine is running, the spring tension cannot be varied, even though a heavier or lighter spring may be required. The entire cutting process must be stopped, if the spring is to be changed. With a controllable fluid pressure, as proposed by the instant invention, the blade to die pressure can be adjusted as light or as heavy as required with a simple fluid pressure regulator.
Pneumatic or hydraulic pressure can be used to vary the force exerted on the spring or other elastic member or material to maintain optimum pressure on the cutter blades toward the die plate. When hydraulic pressure is used, a dedicated hydraulic power unit for controlling the blade to die pressure is required and provisions must be made on or around the equipment to house a hydraulic power unit. Also, a designated control circuit is required for the drive motor on the hydraulic power unit and special care must be taken to prevent hydraulic oil from leaking into the process water, even in the event of a seal failure. When pneumatic pressure is used, installation of an air line is all that is required. In environments where equipment of this nature is installed, compressed air lines are commonly available. Therefore, pneumatic pressure is more simply applied for the present invention, but hydraulic pressure can also be used if desired.